Between centres

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Centres are usually fitted into the lathe by means of morse tapers, which can be quickly and easily fitted, then removed with a knock-out bar.

The traditional drive centre has four prongs (or 'dogs') with a fine centre-locating point. This centre point should protrude about 'Ain (3mm) beyond the prongs, to locate the drive centrally, and have a fine point so that it penetrates the wood easily, allowing the wood to be pushed positively onto t he prongs. Production turners would use an even longer fine point so that they can mount and remove pieces without stopping the lathe. The drive dogs should have a fine edge so that they penetrate the wood to transmit the drive power. This is ideal for a situation where the end face of the wood is square to the lathe axis, as all four prongs will make equal, positive contact with the wood

Wood Lathe Chucks Drive Dog

Above Two-prong centre: no. 1 morse taper and 2-1 Stew.

Right Four-prong drive ccntrc; no. 2 monc taper.

Above Two-prong centre: no. 1 morse taper and 2-1 Stew.

Right Four-prong drive ccntrc; no. 2 monc taper.

Homemade Counterbore

Above Counter bore: no. I morse taper with 2-1 sleeve.

Right Stob drive centre; no. 2 morse taper.

Bolow right Dead tail cup ccntrc used as friction drive: no. 2 morse taper.

Above Counter bore: no. I morse taper with 2-1 sleeve.

Right Stob drive centre; no. 2 morse taper.

Bolow right Dead tail cup ccntrc used as friction drive: no. 2 morse taper.

When the end of the wood is uneven, or not square to the lathe axis, then the two-prong drive centre should be used; it can be positioned so that both the prongs make equal positive contact with the wood. An alternative to the four-prong centre for smaller work is a "steb centre', which is a cup centre with a serrated edge. Its advanlage is that it only leaves a simple ring mark on the wood, which can be acceptable to leave on for some projects. It is available in various sizes to suit the work being turned.

For special situations there are alternative centres. For instance, when turning a lamp that has a hole bored down the middle, a "counter bore' would be used. This is usually a four-prong centre with a long pin, instead of a point, which locates in the hole and gives a secure fixing.

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Taper Turn Between Centres
Above Revolving cone centre suitable for hardwoods; no. 2 morse taper.

60"

90*

30*

: <SL

:

A

60" Point

SO" Point loo blunt

30* Po nt Ico sharp

Will hold hard wood

Will not hold

Wil l eac<ly penetrate

«Curdy

securely

and become loose

Above Revolving cup centre with removable point suitable for soft woods; no. 2 morse taper.

Above Revolving cup centre with removable point suitable for soft woods; no. 2 morse taper.

Woodturning Techniques

Tailstock centres

The tailstock not only supports the wood but also pushes it and holds it firmly onto the drive centre. A revolving centre, rather than a fixed centre, eliminates friction, overheating and burning.

On hardweeds, a simple cone point that penetrates the wood will support It, although the shape of the point is impcrtant. A cone angle of around 90' will provide the support and apply the necessary pressure. A fine point (fine conc angle) will penetrate the wood easily; 'I will continue to penetrate as turning proceeds and the wood becomes loose. A blunt point (large cone angle) won't penetrate enough to hold the wood securely in position under the turning forces and it is likely to come off.

On softwoods, a different design of tail centre is required - a cone point would cause the wood to compress around the cone and to split or become loose. Instead, a cup centre is used; it has a fine point that locates the centre, the ring penetrates to support the wood and the inner cone'flat bottom prevents excessive penetration. The point should be fine and protrude beyond the cup by about '/»in (3mm) for easy location.

A tail cup centre with a removable pin is ideal for long-hole boring. It can be removed when the roughing down is done, to allow the auger to pass through the tailstock and centre to bore the wood. A straight pin would then be placed in the centre point for a secure fixing.

Top left Boring auger through tall centre with point removed.

Middle left Revolving steb tail centre; no. 2 morse taper.

Loft Revolving tail centre with changeable drives.

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Homemade Woodturning

Above 4in faceplate (multi-scrcw chuck); Jour straight holes and four countersunk holes.

Above Forstner bit, used for pin chuck.

Above 4in faceplate (multi-scrcw chuck); Jour straight holes and four countersunk holes.

Above Forstner bit, used for pin chuck.

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